Orbs Keep Aligning to the Balcony Edges

The photos below were taken in Grand Central Terminal in New York (the first one on May 16, 2016 and the next two on May 24, 2016). Each shows a mysterious orb that has aligned itself to either the top or the bottom of a balcony.  I see this kind of "orb aligning behavior" very frequently at this location, much more often than I would expect to see by chance. See here for some astonishing examples.